More than 48 hours to reactivate a SIM

I cancelled my contract with one2one and asked them to please make my sim a pre-paid sim on the 17/09/2018. I was told that this will take 24/48 hours. I phoned again on the 20/09/2018 as the 48-hour mark has now past. They told me that I will receive an SMS with the instructions. On the 28/09/2018, my phone is still not working and now they tell me that MNT has a problem and I need to be patient. I am an Estate Agent and I'm losing a lot of business due to my phone not working. Their service is absolutely horrible and it's unacceptable to wait almost 3 weeks for a phone to be reactivated.